1. Field of the Invention
The present invention relates to a holding sealing material, a method for winding the holding sealing material around an object to be wound, and an exhaust gas purifying apparatus.
2. Discussion of the Background
Exhaust gas discharged from internal combustion engines such as diesel engines contains particulate matter (hereinafter, also referred to as PM). In recent years, there has arisen a serious problem that PM is harmful to the environment and human bodies. Moreover, since exhaust gas also contains toxic gas components such as CO, HC and NOx, there have been growing concerns about influences of these toxic gas components on the environment and human bodies.
In view of these, there have been proposed various exhaust gas purifying apparatuses intended for collecting PM in exhaust gas and for converting the toxic gas components. These exhaust gas purifying apparatuses include: an exhaust gas treating body made of porous ceramics such as silicon carbide and cordierite; a casing for accommodating the exhaust gas treating body; and a holding sealing material that is made of an inorganic fiber aggregate and is disposed between the exhaust gas treating body and the casing. This holding sealing material is used mainly for purposes such as protection of the exhaust gas treating body from damage that may be caused by contact between the exhaust gas treating body and the casing surrounding the exhaust gas treating body as a result of vibrations and impacts during travel of an automobile or the like; and prevention of exhaust gas leakage from space between the exhaust gas treating body and the casing.
This holding sealing material is formed by a mat containing inorganic fibers. The mat has a basic rectangular shape having longer sides along the longitudinal direction and shorter sides substantially perpendicular to the longer sides in a plan view. One of the shorter sides of the rectangular shape has a recess and the other shorter side has a projection having the same shape as the cut-out part of the recess. The mat is wound around the exhaust gas treating body and the projection is fitted into the recess. In this state, the holding sealing material serves to prevent exhaust gas from leaking out.
In recent years, there has been a growing demand for good warming performance of the holding sealing material in order to allow the exhaust gas treating body to effectively exhibit its exhaust gas treating performance by keeping the exhaust gas treating body sufficiently warm. This demand can be satisfied with a structure in which there is a larger space between the exhaust gas treating body and the casing, and the holding sealing material is disposed in the space to prevent heat transfer between the exhaust gas treating body and the casing. To achieve this structure, the holding sealing material should be thicker.
Moreover, in order to make the holding sealing material more firmly hold the exhaust gas treating body, there is also a growing demand for further enhancement of repulsion of inorganic fibers, which is a factor contributing to holding ability. To meet this demand, the weight per unit area (basis weight) of the holding sealing material should be increased.
The thickness or weight per unit area (basis weight) of the holding sealing material can be increased by increasing the thickness of the mat of the holding sealing material. However, in recent years, multi-layer mats obtained by laminating a plurality of mats have been used to increase the thickness or the basis weight of the holding sealing material, instead of changing the mat thickness.
In the case that such a holding sealing material including a plurality of mats is wound around the exhaust gas treating body, the projection and the recess of each mat should be successfully fitted to each other under proper control of the tension in the mats.
JP-A 2007-218221 and JP-A 2009-264186 listed below disclose holding sealing materials of a multi-layer structure designed with consideration for fitting between the projections and the recesses.
JP-A 2007-218221 recites a holding sealing material (monolith holding material) designed such that laminated mats can be wound around a monolith without looseness of the mats with fitting parts on both sides of each mat fitted to each other (Claim 1). JP-A 2007-218221 also teaches that in order to secure the above performance of the holding sealing material, the laminated mats are fixed to one another with at least one end being freely movable (Claim 3).
JP-A 2009-264186 discloses a holding sealing material in which a plurality of mats have a longitudinal length that sequentially increases with the order of lamination, the mats are fixed with one another at two or more fixed parts, and at least two of the fixed parts are located at different positions in the longitudinal direction in a side view.
The contents of JP-A 2007-218221 and JP-A 2009-264186 are incorporated herein by reference in their entirety.